Removing an electron from an atom forms a positive ion. Positive ions produced in this way are used for various processing units and analyzers such as impurity ion implantation equipment used for manufacturing semiconductor devices and dry etching equipment using plasma discharge involving ions and electrons. Ion implantation equipment turns n- or p-type impurities into positive ions to implant impurity ions of a given amount into the doping region of a semiconductor substrate of a semiconductor device.
By the way, that which has more than two electrons removed, such as, e.g., Xe44+ ion, is called a positive multicharged ion, which has an extremely large internal energy. It is known that bombarding multicharged ions on a solid surface causes many peculiar phenomena such as emission of a large number of secondary electrons (see Non Patent Literature 1 in the list below) and giving rise to a large structural change in nanometer size around a point of incidence of the multicharged ions (see Non Patent Literature 2 in the list below).
Unique interactions of such multicharged ions with a material have focused the spotlight of attention upon their feasible application to processes in a nanometer region such as single-ion implantation and fabrication of a quantum dot (see Non Patent Literature 3 in the list below).
As the ion source from which to produce such multicharged ions there are generally known electron cyclotron resonance (ECR) type ions generating source (ECRIS) and electron beam type ions generating source (EBIS), the latter being featured by high degree of ionization of ions obtained.
As an EBIS there is known an apparatus of the National Institute for Fusion Science that has been developed for researches in the atomic physics (see, e. g., Non Patent Literature 4 in the list below). This apparatus comprises an electron source (cathode), a drift tube, a collector, a solenoid magnet and an ion extracting lens so configured that electrons exiting the cathode are passed through the drift tube and collected by the collector. The electrons are compressed by a strong magnetic field formed in the drift tube, becoming an electron beam of large current density. On the other hand, a gas introduced from the vicinity of the cathode becomes multicharged ions by impact ionization of electrons, because a square well potential is formed in the drift tube to be a barrier to ions.
In 1988 EBIT (electron beam ion trap) was developed which was improved over the EBIS (see Non Patent Literature 5 in the list below). The EBIT which is identical in principle of generating multicharged ions to the EBIS uses a superconducting Helmholtz type coil and a reduced length of the drift tube such as to avoid the instability of plasma in the drift tube, thereby improving the confinement time for ions so that the high multivalent multicharged ions can stably be retained. As a consequence, in the EBIT it has been made possible to squeeze an electron beam in the drift tube to the ultimate to form highly ionized ions.
As an EBIT there has also been developed by the present inventors an apparatus (see Non Patent Literature 6 in the list below) that has an electron accelerating voltage of 300 kV at its maximum to allow completely ionizing uranium (U). This EBIT was developed for researches in the atomic physics and has the highest performance in the world as the internal energy of multicharged ions that can be produced.
By the way, as a method of analysis using ions, secondary ion mass spectrometry (SIMS), which uses monovalent ions as a sputter source, is conventionally known.
Surface analysis using slow multicharged ions as a sputtering source described above was attempted (see Non Patent Literature 7). Non Patent Literature 7 discloses the detection of H+ ions (protons) obtained when multicharged ions having a valence of 4 to 12 were irradiated onto the surface of Si at the speed as low as 2 keV to 5 keV.